Thermally stabilized hydrocarbon liquid compositions



United States Patent 3,419,368 THERMALLY STABILIZED HYDROCARBON LIQUID COMPOSITIONS Arnold M. Leas, Ashland, Ky., assignor to Ashland Oil & Refining Company, Houston, Tex., a corporation of Kentucky N0 Drawing. Continuation-impart of application Ser. No. 275,865, Apr. 30, 1963. This application Jan. 23, 1967, Ser. No. 610,764

15 Claims. (Cl. 44-70) ABSTRACT OF THE DISCLOSURE A hydrocarbon liquid composition, particularly useful as a jet fuel, including a major proportion of a hydrocarbon liquid and a minor proportion of the combination of ethylene glycol monobutylether acetate and an alkanol ester of citric acid, such as tributyl citrate, acetyl tributyl citrate, and triethylhexyl citrate, an N,N-salicylidene alkyldiamine, such as N,N-salicylidene propane diamine, or N,N-disalicylidene ethane diamine, and mixtures of such esters and diamines. The composition may also include a conventional de-icing additive, a conventional antioxidant or a mixed polyamine jet fuel additive.

The present application is a continuation-in-part of application Ser. No. 276,865, filed Apr. 30, 1963, and now abandoned.

The present invention relates to novel hydrocarbon liquid compositions such as jet fuels, hydraulic fluids and lubricants and other crude oil derivatives. In a more specific aspect, the present invention relates to hydrocarbon liquid compositions, including jet fuels, hydraulic fluids and lubricants of improved properties, particularly, storage and thermal stability and lubricity.

It is generally an accepted fact that the manufacture of jet fuels is a most demanding proposition and that any additives for hydrocarbon compositions which produce a stable jet fuel of good lubricity characteristics will likewise be capable of producing other hydrocarbon liquids similarly stable and of good lubricity characteristics. Accordingly, the present discussion will be confined primarily to jet fuels with the understanding that the compositions of the present invention are useful in other environments having specifications which are less stringent.

Hypothetically, the shortest distance between two points would be to connect the production nozzle of a refinery producing jet fuel to the inlet of the combustion nozzle within a jet engine. However, this is obviously physically impossible and to approach it is highly impractical. It must be recognized that refiners or producers of fuel need to blend, store, test and schedule loading and transportation to meet the needs of a customer who, in turn, will need to store a sufficient quantity for normal usage and unexpected contingencies. In most instances, the fuel in question will have had an opportunity to degrade and accumulate contaminants during storage and transit. This fuel incipient degradation period, during storage and transit, provides time for most deleterious, dynamic physical, chemical and biological kinetic reactions to complete their offensive deterioration of the fuel. In addition, it must be recognized that fuels can vary considerably when originating from many different crude oil sources, refinery processes, shipping and storage containers, fuel handling procedures, testing procedures and additive treatments and for these reasons fail to meet specifications.

It has heretofore been proposed that the by-products of storage and/or transportation or other contaminants be removed from the fuel at the use point loading tank farm. conventionally, a plurality of what are known as 3,419,368 Patented Dec. 31, 1968 filter coalescers are used in series at the aircraft loading tank farm. However, these filter coalescers have failed to properly process supersonic jet fuels, inasmuch as such fuels must now be essentially free of soluble chemical and biological contaminants, as well as insoluble sediment and water when delivered to the aircraft; and this is a case of cure rather than prevention.

More expensive alternatives to the use of the filter coalescer, or, in addition to the filter coalescer, which have been proposed, include, over-refining at the production point, redesigning aircraft engines, speeding the fuel from the refinery in clinically clean facilities and maintaining minimal contact with oxygen during transport. Another approach is the development of additional, new all-purpose additives which will overcome the problems of origin, production, transportation and storage. It is this last approach to which the present invention is directed.

A thermally stable jet fuel is defined by the industry as a fuel which leaves no visible varnish deposits on heat exchanger metal surfaces and does not form solid particles, tending to plug jet engine fuel filters or fuel injection nozzles.

It is well known to those familiar with this art that thermal stability for jet fuels is the most difficult quality to obtain and maintain in practice, yet it is the most important property of the fuel to control.

Jet engines, and particularly the engines of supersonic and hypersonic jet aircraft, are operated at extremely high temperatures. In such use, the fuel is often used as a heat sink for the aircraft via the heat exchangers and injection nozzles in the engine. The fuel may also be subjected to elevated temperatures, during storage in wing tanks on supersonic aircraft, resulting from the absorption of heat from the surface of the wing. In some cases, the fuel may be subjected to elevated temperatures, for several hours prior to combustion, in the range of 400 to 700 F. for supersonic aircraft and to considerably higher temperatures up to the point of initiation of endothermic reactions for hypersonic aircraft. Many, if indeed not all, jet fuels tend to be relatively unstable when subjected to high temperatures below the combustion point, thus tending to form heavy solid or semisolid particles which, in turn, cause heat exchanger fouling, jet nozzle plugging and other undesirable effects. Fuel thermal instability not only reduces the operational life of the engine but may present a hazard to flight operation. Accordingly, a very serious need to improve the thermal stability of a wide range of jet fuels has arisen.

The thermal stability of jet fuels is measured in the industry by the so-called ASTM-CRC standard, modified CRC, and research CRC coker tests. In these tests, the fuel is subjected to conditions generally simulating the adverse conditions to which it is subjected in actual use. In the research coker test, for example, the fuel is heated in a reservoir to a temperature corresponding to the temperature of fuel in the aircraft wing tanks. (In the standard coker test, a heated reservoir is not used, thus, this arrangement corresponds to aircraft when the fuel is essentially at ambient temperatures in the tanks.) From the reservoir the fuel is pumped through a preheater tube at a higher temperature, corresponding to the temperature of the heat exchanger in the jet engine, and on through a filter at a still higher temperature, corresponding to the temperature at the entrance to the combustion nozzle. This filter removes nonliquid particles which have been found at the elevated temperatures. The hot filter simulates the conditions to which the fuel is subjected as it passes through the fuel injection nozzles in the engine immediately prior to combustion. The operating conditions of the test can be varied to correspond to various use conditions. Coker test conditions are usually expressed in ab- 3 breviated form; for example, 200-400/500/6, meaning that the reservoir temperature is 200 F., the preheater temperature 400 F., the filter temperature 500 F., and the fuel flow rate 6 pounds per hour.

At the present time, fuels to be used in Mach 3 plus jet aircraft utilize coker conditions of 300-500/600/ 6, and, in the future, it is expected that these conditions will be further increased in severity to 300-600/ 700/ 6.

The results of the coker tests are expressed in terms of a rating code, indicating relatively the quantity of varnish deposit left in the preheater, ranging from for the best, to 8, for the worst, and in terms of the pressure drop in inches of mercury across the filter, ranging from 0, for the best, to 25 inches for the worst. The high thermal stability demanded of Mach 3 plus jet fuels is indicated by the fact that they must have a preheater code rating less than 3 and a filter drop of less than 5 inches of mercury.

It is therefore an object of the present invention to provide a hydrocarbon composition which solves all of the above mentioned problems. Another object of the present invention is to provide a new group of additives for liquid hydrocarbons, particularly jet fuels, hydraulic fluids and lubricants. Still another object of the present invention is to provide a new group of additives for hydrocarbon liquids, including jet fuels, hydraulic fluids and lubricants which are suitable for use either at the point of production or at the point of use. A still further object of the present invention is to provide a new group of additives capable of converting a good hydrocarbon liquid, particularly aircraft fuel, into a better quality product, Another and further object of the present invention is to provide a new group of additives for hydrocarbon liquids, particularly aircraft fuels, which will permit the use of hydrocarbon products from a wide variety of crude oil sources; which have been subjected to a wide variety of refining processes; which have been shipped and stored in a large number of different containers; and which have been subjected to a large number of different handling procedures, test procedures and additive treatments. A further object of the present invention is to provide an improved hydrocarbon liquid composition suitable for use as aircraft fuels which will result in a minimum rejection of fuels and make possible maximum in-flight safety with minimum tankage and inventory at the point of use. A still further object of the present invention is to provide a new group of additives for hydrocarbon liquids, particularly aircraft fuels, hydraulic fluids and lubricants which proor in combination with other hydrocarbon liquid additives. It has further been found, in accordance with the present invention, that a synergistic effect is obtained if the subject ethylene glycol monobutylether acetate is combined with certain polyamine and substituted polyamine additives, or certain other conventional hydrocarbon liquid additives.

The novel additives of the present invention have been found to improve the thermal stability and lubricity characteristics of hydrocarbon liquids in general and, specifically, jet fuels, hydraulic fluids, lubricants and other hydrocarbon liquids and derivatives of crude oils. These new additives, when incorporated in hydrocarbon liquids, particularly jet fuel compositions, have been found to be much more effective than conventional antioxidants or metal deactivators. Specifically, it has been found that conventional antioxidants and metal deactivators become thermally unstable when heated to temperatures in the neighborhood of 300 to 600 F. The decomposed byproducts of these additives and the fuel itself become potential causes of nozzle clogging and varnish formation in jet engines since such engines are subjected to prolonged preheating before actual combustion of the fuel. The additives of the present invention have been found to extend the thermal stability limits of jet fuels to the range of 500 F. to 800 F. and even higher. These additives retard the formation of high temperature degradation products from additives of conventional types that may be present in the fuel and from the fuel itself and prevent such products, if formed, from causing instability effects, including varnish and other deposits on the engine fluid passages, thereby enabling fuels to withstand higher temperatures in the engine prior to combustion.

Specifically, it has been found that the thermal stability of a fuel can be improved by incorporating in the fuel from about 0.0001 to 2% by volume and, preferably 0.01 to 0.1% by volume of butyl Cellosolve actate, as ethylene glycol monobutylether acetate and esters of citric acid, either at the production point and/or the use point. The following examples illustrate the effectiveness of these particular additives alone.

In the following table, the butyl Cellosolve acetate, as ethylene glycol monobutylether acetate, is designated BCA, tributyl citrate as TBC, acetyltributyl citrate as ATC, and tri-2-ethylhexyl citrate as TEHC. The antioxidant referred to is 2,6-ditertiary-butyl-paracresol which is a conventional jet fuel additive.

TABLE I Test Results Additive, Fuel and Test# 1b./1,000 bbls. Coker Test Filter,

fuel Conditions Preheater Differential Codeffi Pressure,

in., Hg

300-500/600/6 3 19. 1 300-500/600/6 2 0. I 300-500/600/ 6 4 1. 2 2. Mach 3 0 0. 4 Mach 3 plus 31b./1 7 12. 5 3. Mach 3 plus 3 lb./l, 4 4. 4 4. Mach 3 plus 3 Ill/1,000 bbls. Antioxidant. 30(Hi00/700/6 5 6. 3 5. Mach 3 plus 3 lb./l,000 bbls. Antioxidant- 300-600/700/ 6 4 5. 7 6. Mach 3 plus 3 lb./1,00D bbls. Antioxidant. 300-600/700/6 4 8. 4 7. Mach 3 plus 3 DEL/1,000 bbls. Antioxidant. 300-600/700/6 4 10. 5

duce a thermally stable product. An additional object of the present invention is to provide a new group of additives for hydrocarbon liquids, particularly aircraft fuels, hydraulic fluids and lubricants which improve the lubricity thereof.

In accordance with the present invention, the novel hydrocarbon composition of the present invention includes a major portion of a hydrocarbon liquid and a minor proportion of an additive comprising, butyl Cellosolve acetate, as ethylene glycol monobutylether acetate, and certain esters of citric acid in combination with one another It has also been found that a synergistic improvement of the thermal stability of hydrocarbon liquids, particularly jet fuels, can be obtained if ethylene glycol monobutylether acetate is combined with certain known polyamine additives. More specifically, these additives are known as metal deactivators and additives for jet fuels. For example, a commercially available metal deactivator (50 to active ingredient) of an N,N'-disalicylidene- 1,2-alkyldiamine, such as N,N-disalicylidene-1,2-propanediamine or its homolog N,N'-disalicylidene-l,Z-ethanediamine, can be combined with ethylene glycol monobutylether acetate to further improve the high temperature thermal stability of hydrocarbon liquids and, particularly jet fuels.

The preferred blend of these two compounds includes about 85 to 99% by volume of ethylene glycol monobutylether acetate and about 15 to 1% by volume of the 6 0.0001 to 2% by volume of the total fuel and, preferably, between about 0.01 and 0.1% by volume.

The effectiveness of this particular combination of the additives with various fuels is illustrated by the following 5 examples, when compared with the utilization of the ether or citrate additives alone.

TABLE IV Additive, Percent by Vol- Test Results ume of Total Additive Fuel Test and lbs. additive.1,000 bbl. fuel Coker Test Conditions Filter Additive A Additive B Preheater Differential Code Pressure,

in., Hg

Mac 0 300-500/600/6 3 19. 1 1. Mach 3 plus 50. loo-BOA. o 3oo-5oo/eoo/e 2 0.1 Mac a 0 300-500/600/6 4 1. 2 2. Mach 3 plus 50. 300-500/60 6 0 0. 4 Mach 3 300-500/600/6 7 3. 9 3. Mach 3 plus 50 300-500/600/6 2 0.1 Mach 3 300-500/600/6 5 20. 2 4. Mach 3 plus 50. 300-500/600/6 1 0. 0 Parafiinic Jet FueL 300-500/ 600/ 6 5 2. 5 5. Parafilnie Jet Fuel plus 50. 300-500/600/6 1 0. 1 Mach 3 plus S-antioxidant 300-600/ 700/6 7 l2. 5 6. Mach 3 plus 8-antioxidant plus 60 300-600/700/6 4 4. 4 7. Mach 3 plus S-antioxidant plus 50 100BCA 0 300-600/700/6 5 6. 3 8. Mach 3 plus 8-antioxldant plus 0 100-IBC. 300-600/700/6 4 5. 7 9. Mach 3 plus 8-antioxidant plus 50. 75BOA -TBC 300-600/700/6 l 0. 8 10. Mach 3 plus 8-antioxidant plus 20- O 100-A'IC 300-600/700/6 4 8. 4 l1. Mach 3 plus 8-antioxidant plus 50 75BOA 25-ATC H. 300-600/700/6 2 2. l 12. Mach 3 plus 8-antioxidant plus 20 0 100-IEHC. 300-600/700/6 4 10. 5 13. Mach 3 plus S-antioxidant plus 50 75-BCA. 25-TEHC 300-600/700/6 1 2. 2

Finally, it has also been found that a synergistic effect may be obtained if the ethylene glycol monobutylether acetate and esters of citric acid are combined with the previously mentioned polyamine additives.

The relative proportions of the three components would be as follows 25 to 75 percent of ethylene glycol monobutylether acetate; 1 to 15 percent of the polyamine compound; and 25 to 75 percent of the ester of critric acid. This three component mixture is advantageously added to the liquid hydrocarbon, particularly a jet fuel, in amounts of about 0.0001 to 2% by volume TABLE II Test Results Additive, Percent by Fuel Test and lbs. additive/1,000 bbl. fuel Volume of Total Additive Coker Test Filter Conditions Preheater Differential Additive A Additive B Code Pressure, in., Hg

Mach 3 0 300-500/600/6 7 25 1. Mach 3 plus 100. 96BOA 4MD 300500/600 1 0 2. Mach 3 plus 100- C D 300-500/600/6 3 0. 2 Kerosene 0/ 6 0. 3. Kerosene plus 100- 2 0. 1 Kerosene 7 21. 4 4. Kerosene plus 100 2 1.8 Parafiinic Jet Fuel 4 2. 6 5. Parafiinic Jet Fuel plus 60- 2 0.0 Mach 3 plus s-antioxidant 7 12. 5 6. Mach 3 plus S-antioxidant plus 60... 4 4. 4 7. Mach 3 plus S-antioxidant plus 2 0 6 10.2 8. Mach 3 plus 8-antioxidant plus 60 96-BCA 4-MD 300-600/700/6 2 2. 6

The ethylene glycol monobutylether acetate additive of the present invention has also been found to have a synergistic effect on the thermal stability of hydrocarbon liquids and, particularly jet fuels, if combined with the previously mentioned esters of citric acid.

Specifically, the esters of citric acid found useful in accordance with the present invention include tributyl citrate, acetoxytributyl citrate, acetoxytri-Z-ethylhexyl citrate, etc.

A blend of the citrate and the ether preferably includes about 25 to by volume of citrate and 75 to 25% by volume of ether. This blend may be added to a hydrocarbon liquid, such as a jet fuel, in amounts of about 75 of the total fuel and preferably between about 0.01 and 0.1% by volume.

The following examples illustrate the advantages of the three component mixture in various fuels and as compared with any two of the three and this combination when using both N,N'-disalicylidene-1,2-propane diarnine and IPA-5 (a commercial jet fuel additive, comprising a mixture of polyamines). The prestressed fuel is a fuel previously subjected to a temperature of 300 F. for 48 hours to simulate storage in the wing tanks of a supersonic jet during a mission. The deicer is a conventional additive for this purpose, ethylene glycol monoethyl ether, and the antioxidant is a conventional additive, 2,6-ditertiar-y-butyl-paracresol.

TABLE V Additive, Percent by Volume of Total Additive Filter Fuel, Test and lbs. additive/1,000 bbl. fuel Coker Test Pro-Heater Differentia Additive A Additive B Additive C Additive D Conditions Code Pressfire,

in., g

Mach 3 0 0 300-500/600/6 0.1

1. Mach 3 plus 100.-- 300-500/600/6 2. Mach 3 plus 200- 300-500/600/6 Mach 3 300-500/600/6 5 3. Mach 3 plus 100. 300-500/600/6 2 4. Mach 3 plus 200-.- 300-500/600/6 1 Prestressed Mach 3 300-500/600/6 5. Prcstressed Mach 3 plus 200. 300-500/600/6 2 JP-6 300-500/ 600/ 6 9 6 J P6 plus 100..

Parathnic Jet F 5 Parailinic Jet Fuel 8. Parafiinic Jet Fuel plus Parafiinic Jet Fuel 9. Paraifinie Jet Fuel plus 60 Paratiinic Jet Fuel :1; 0.12% deicer 10. Parafi-inic Jet Fuel :1: 0.12% deicer plus 60 Mach 3 plus 8 Antioxidant 11. Mach 3 plus 8 Antioxidant plus 50..

. Mach 3 plus 8 Antioxidant plus 50. Mach 3 plus 8 Antioxidant plus 50-. Mach 3 plus 8 Antioxidant plus 22. Mach 3 plus 8 Antioxidant plus 50.. Mach 3 plus 8 Antioxidant plus 12. Mach 3 plus 8 Antioxidant plus 12- Mach 3 plus 8 Antioxidant plus 50. Mach 3 plus 8 Antioxidant plus 50. Mach 3 plus 8 Antioxidant plus 50. Mach 3 plus 8 Antioxidant plus 22. 0

. Mach 3 plus 8 Antioxidant plus 50 -B CA..

In runs 1 through 5 above, the butyl Cellosolve acetate plus half the diamine was added at the production point, the fuel was filtered at the use point, and the citrate plus the other half of the diamine was added after filtration.

The novel additives of the present invention are compalible with approved conventional jet fuel additives and may be used in combination with them in order to impart better, high temperature stability characteristics to Fuel, Test and Liquid Volume Additive in Fuel 300-600/ 700/ 6 300-600/ 700/ 6 300-600/700/ 6 -5. 300-600/ 700/ 6 QQJFA-fi- 300-600/700/6 6-JFA-5. 300-600/700/6 0 JFA-5-.- 300-600/700/6 0 JFA5 300-600/700/6 6-1 FA-5. 300-600/700/6 6JFA-5 300-600/ 700/ 0 lowing examples illustrate the improvement in lubricity, as measured by the Ryder Gear Test, which is effected by the presence of the additives of the present application. The results of these tests indicate that a fine film is produced on hot metal bearing surfaces which provides the necessary lubrication for these surfaces and is responsible for greatly increasing pump life. The use of the additives of the present application can be justified on this basis alone in some cases.

TABLE VI Additive, by Volume of Total Additive Ryder Gear Test,

lbs/lineal in. Additive A Additive B Additive O Maoh3 0 0 O 222 1 Mach 3 plu BCA... 25'IBC-.. 0 1, 045 Mach 3 O 0 0 156 2. Mach 3 plu 804 Parailinic Jet Fuel. 3. Parafiinic Jet Pu 527 Paraflinic Jet Fuel 4. Parafiinic Jet Fuel plus 0.5%.. 578 Paralfinie Jet Fuel plus 0.12% deicer. 0 0 0 5. Paratfmic Jet Fuel plus 0.5% ts-BOA.-- 48TBO. 4-MD 566 the fuel than can be obtained with the conventional additives alone. As is obvious from the previous examples, the additives of the present invention are quite effective in improving the thermal stability of otf-specification fuels, either containing conventional additives or having no conventional additives. The additives are also preferably used in combination with conventional anti-icing additives and the following example shows the combination of the present application with an ethylene glycol monoethylether as an anti-icing agent.

One of the surprising results of the use of the present additives is that the lubricating qualities of the fuel are substantially improved by their presence. The relative lubricating qualities of a liquid can be described quantitatively in terms of the well-known Ryder Gear Test, wherein a standard set of gears is driven over a predetermined operating period with the gears immersed in the fluid undergoing test. The results of this test are expressed as a gear tooth pressure per lineal inch necessury to achieve a certain degree of scarring on the gear teeth. In pumping hot fuels, particularly jet fuels,'a critical maintenance problem ordinarily arises in the pump because of the lack of lubrication where the hot fuel contacts metal-to-metal bearing surfaces. The fol- While, as indicated, the additives of the present application can be incorporated in the hydrocarbon liquid, particularly a jet fuel, at the use point, it should also be understood that these additives may be incorporated in a hydrocarbon liquid at the production point and prior to any appreciable storage of the liquid. Preferably, these additives are incorporated in the freshly produced hydrocarbon liquid at the refinery in limited amounts for protection during transportation and storage and, thereafter, the fuel or other hydrocarbon liquid is filtered to remove undesired degradation products which have formed, and finally, a second proportion of these additives is incorporated in the liquid just prior to its use.

I claim:

1. An improved hydrocarbon liquid composition comprising, a major proportion of a hydrocarbon liquid and a minor proportion, sufficient to improve the thermal stability of said hydrocarbon liquid, of the combination of ethylene glycol monobutylether acetate and an additive material selected from the group consisting of an alkanol ester of citric acid and an N,N'-salicylidene alky-ldiamine.

2. A composition in accordance with claim 1 wherein the additive is an alkanol ester of citric acid.

3. A method in accordance with claim 2 wherein the ester is tributyl citrate.

4. A composition in accordance with claim 2 wherein the ester is acetyl tributyl citrate.

5. A composition in accordance with claim 2 wherein the ester is triethylhexyl citrate.

6. A composition in accordance with claim 1 wherein the additive is N,N'-salicylidene alkyldiamine.

7. A composition in accordance with claim 6 wherein the diamine is N,N'-salicylidene propane diamine.

8. A composition in accordance with claim 6 wherein the diamine is N,N'sa1icy1idene ethane diamine.

9. A composition in accordance with claim 1 wherein the additive is a mixture of an alkanol ester of citric acid and an N,N'-salicylidene alkyldiamine.

10. A composition in accordance with claim 9 wherein the ester is tributyl citrate.

11. A composition in accordance with claim 9 wherein the ester is acetyl tributyl citrate.

12. A composition in accordance with claim 9 wherein the ester is triethylhexyl citrate.

References Cited UNITED STATES PATENTS 2,684,292 7/1954 Caron et a1. 4472 XR 3,068,083 12/1962 Gee et a1. 44 7o 3,103,101 9/1963 Jatfer 44-77 XR DANIEL E. WYMAN, Primary Examiner.

\V. I. SHINE, Assistant Examiner.

US. Cl. X.R. 44-73; 25252, 79 

